Flutter bloc 状态未发出或更新。从未调用方法 mapEventToState

Question

以下代码在使用 flutter_bloc 4.0.1 的 null 安全性之前工作，但在 null 安全性迁移之后，状态没有按照 flutter_bloc 7.3.3 的预期更新/发射/广播。

永远不会调用下面的 _reactToState 和 mapEventToState 方法。我该如何解决？

启动画面

class SplashScreen extends StatefulWidget {
  final Strapper strapper;
  final Service? service;

  SplashScreen(this.strapper, this.service);

  @override
  State<StatefulWidget> createState() => _SplashScreenState();
}

class _SplashScreenState extends State<SplashScreen> {
  SplashBloc? _splashBloc;

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    if (_splashBloc == null) {
      _splashBloc = SplashBloc(widget.strapper, widget.service);

      _splashBloc!.stream.listen(_reactToState);
    }
  }

  @override
  dispose() {
    _splashBloc?.close();
    _splashBloc = null;
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return BlocProvider<SplashBloc>(
      create: (context) => _splashBloc!,
      child: BlocBuilder<SplashBloc, SplashBlocState>(
        builder: (context, state) => Container(
          child: Stack(
            children: <Widget>[
              LogoPanel(
                _showWidgetForState(state),
              ),
            ],
          ),
        ),
      ),
    );
  }

  void _reactToState(SplashBlocState state) {
    if (state is InitializingSplashBlocState) {
      if (widget.logOut) {
        _splashBloc!.add(LogoutSplashBlocEvent());
      } else {
        _splashBloc!.add(CInitializationSplashBlocEvent());
      }
    } else if (state is AuthSuccessSplashBlocState) {
      App.navigateToSomewhere(context, state.isNewUser);
    }
  }

  Widget _showWidgetForState(SplashBlocState state) {
    if (state is InitializingSplashBlocState) {
      return _getProgressIndicator();
    } else if (state is ChooseSomethingSplashBlockState ) {
      return _showSignInWidget();
    }
  }
}

飞溅区

class SplashBloc extends Bloc<SplashBlocEvent, SplashBlocState> {
  final Strapper? strapper;
  final Service? service;

  SplashBloc(this.strapper, this.service) : super(InitializingSplashBlocState());

  @override
  Stream<SplashBlocState> mapEventToState(event) async* {
    if (event is CInitializationSplashBlocEvent) {
      await strapper!.run();
    }
    bool chooseSomething = !service!.hasSomeSelection;

    if (chooseSomething) {
      yield ChooseSomethingSplashBlockState();
    } else if (event is RAuthSplashBlocEvent) {
      yield AuthSplashBlocState();
      var authState = await _run();
      yield authState;
    } 
  }

  Future<SplashBlocState> _run() async {
    // Do something
  }
}

Splash Bloc 活动

abstract class SplashBlocEvent extends Equatable {
  const SplashBlocEvent();

  @override
  List<Object> get props => [];
}

class CInitializationSplashBlocEvent extends SplashBlocEvent {}

class RAuthSplashBlocEvent extends SplashBlocEvent {}

Splash Bloc 状态

abstract class SplashBlocState extends Equatable {
  const SplashBlocState();

  @override
  List<Object> get props => [];
}

class InitializingSplashBlocState extends SplashBlocState {}

class AuthSplashBlocState extends SplashBlocState {}

class ChooseSomethingSplashBlockState extends SplashBlocState {}    

class AuthSuccessSplashBlocState extends SplashBlocState {
  final CurrentUser? user;
  final bool isNewUser;

  AuthSuccessSplashBlocState(this.user, this.isNewUser);
}

Answer 1

根据documentation：

在v6.0.0中，上面的sn -p不输出初始状态，只输出后续的状态变化。以前的行为可以通过以下方式实现：

final bloc = MyBloc();
print(bloc.state);
bloc.listen(print);

所以我在初始屏幕中更改了我的代码，如下所示：

@override
  void didChangeDependencies() {
    super.didChangeDependencies();
    if (_splashBloc == null) {
      _splashBloc = SplashBloc(widget.strapper, widget.service);
      _reactToState(_splashBloc!.state); // Added this line 
      _splashBloc!.stream.listen(_reactToState);
    }
  }

就是这样。有效！ _reactToState 和 mapEventToState 肯定会被调用。

Answer 2

当您使用 Streamcontrollers 时，它大大简化了状态。我构建了一个块代码来管理状态。 materialapp 子项是 splashWidget，其工作是从发出 Time 状态的 bloc 代码中渲染小时、分钟、秒。如果用户单击初始屏幕或经过 5 秒，则初始屏幕将替换为 HomePageWidget。 bloc 代码使用 timerState 事件控制定时器的启动和停止。

'package:flutter/material.dart';
import 'bloc_splash.dart';
import 'main.dart';

class SplashWidget extends StatelessWidget {
  const SplashWidget({Key? key}) : super(key: key);

_redirectToHome(BuildContext context)
{
  Navigator.pushReplacement(context,MaterialPageRoute(builder:(_)=>MyHomePage(title:"helloWorld")));

}
String _displayClock(Time ? data)
{
  String retVal="";
  if (data!=null)
  {
    retVal="Time: ${data.hour} : ${data.minute} : ${data.second}";
  }
  return retVal;

}
  @override
  Widget build(BuildContext context) {

    SplashBloc _bloc=SplashBloc();
    _bloc.timerOnChange(StartTimer());
   
    return Scaffold(

      body:InkWell(
              onTap: (){_bloc.timerOnChange(StopTimer());
              _redirectToHome(context);
              },
              child:Container(
                  child: 
          StreamBuilder<TimeState>(
            stream:_bloc.timeStream,
            builder:(context,snapshot)
            {
              if(snapshot.hasData && (snapshot.data is RedirectState))
              {
                return MyHomePage(title:"helloWorld");
              }
              return Center(child:Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                Text("Splash Screen", style:TextStyle(fontSize: 24,fontWeight: FontWeight.bold)),
                Text(_displayClock(snapshot.data?.time)),
              ]));
            }
          )
      ))
    );
  }
}

块代码

import 'package:equatable/equatable.dart';
import 'package:flutter/material.dart';
import 'package:rxdart/rxdart.dart';
import 'dart:ui';
import 'dart:async';

abstract class TimerEvent extends Equatable{
  const TimerEvent();
  @override 
  List<Object>get props=>[];
}
class StartTimer extends TimerEvent{
  const StartTimer();
}
class StopTimer extends TimerEvent{
   const StopTimer();
}

class Time{
  final int hour;
  final int minute;
  final int second;
  Time(this.hour,this.minute,this.second);
}
class TimeState extends Equatable{
  final Time time;
  TimeState(this.time);
  @override
  List<Object> get props=>[time];
}
class RedirectState implements TimeState{
  final Time time;
  RedirectState(this.time);
  @override
  List<Object> get props=>[time];

  @override
  // TODO: implement stringify
  bool? get stringify => throw UnimplementedError();

}

class TimerState extends Equatable{
 final bool started;
 const TimerState(this.started);
 @override 
 List<Object> get props => [started];
}

class SplashBloc
{
   SplashBloc();
   Timer ?_timer;
   var countDown=5;
   Stream<TimeState> get timeStream=> _timeController.stream;
   final _timeController =BehaviorSubject<TimeState>();
   void dispose()
   {
      _timeController.close();
   }
   void _pushTimeOnTheStream(Timer timer)
   {
     DateTime now=DateTime.now();     
      _timeController.sink.add(TimeState(Time(now.hour,now.minute,now.second)));
      this.countDown-=1;
      if (this.countDown==0)
      {
        timerOnChange(StopTimer());
      _timeController.sink.add(RedirectState(Time(0,0,0)));
      }
   }
   void timerOnChange(TimerEvent event) { 
    if (event is StartTimer)
    {
      _timer=Timer.periodic(Duration(seconds: 1),_pushTimeOnTheStream);
    }
    else if(event is StopTimer){
       //_timerController.sink.add(TimerState(false)); 
       _timer?.cancel();
    }
 } 
}

应用程序

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const SplashWidget(),
    );
  }
}